This invention directs itself to fluid control valves, and more particularly to pinch valve systems for controlling fluid flow in a fluid flow path.
Various types of control valves have been developed for use in plumbing, drainage and other fluid flow applications and systems. It is known that pinch valves systems are particularly suited for controlling fluid flow in vacuum-line systems.
In pinch valve systems, a critical component is the tubular elastic sleeve member that is pinched to occlude the fluid flow. The design of the elastic sleeve member is plagued with a plurality of service problems.
In many prior art systems, when the elastic sleeve member is pinched, the sleeve member is stretched and is subjected to undue stresses. Over repeated use, the stresses can result in fatigue of the elastic material, and eventually lead to a tear in the elastic sleeve member, thereby rendering the pinch valve system useless.
Moreover, particularly in vacuum-line systems, the elastic sleeve member is susceptible to exposure to boiling fluids. It is known to the art that the temperature at which a fluid boils decreases as the surrounding pressure decreases and vice-versa. In vacuum-line systems, the pressure applied to the fluid is below atmospheric pressure and the fluid can experience boiling conditions at significantly lower temperatures. Hence, when a pinch valve system is opened in the presence of warm fluids that were previously below boiling point, the sudden drop in pressure applied to the fluid can cause the fluid to boil almost instantly. Over repeated use, the vigorous boiling actions of the fluids can cause surface vitrification and material hardening of the sleeve member. The surface vitrification, characterized by tiny pits and holes, and hardening of the material become points of weakness from which a tear can propagate, thereby reducing the service life of the sleeve member.
Additionally, fluid flows in plumbing and drainage systems can contain caustic chemicals, oils, fats and the like. While these chemicals, oils and fats can have deleterious effects on the elastic sleeve member even at ambient conditions, the deleterious effects are further exacerbated when the fluids experience boiling conditions.
Finally, fluid flow in plumbing or drainage systems often contains solids such as refuse from food preparations, coffee grounds and the like. In vacuum-line systems, the fluid flow travels at high speeds and the impact of these solids on the elastic sleeve member can cause damage to the sleeve member.
It is known to the art that fluorocarbon materials such as polytetrafluoroethylene, polyvinylidene fluoride, polytrifluorochloroethylene and the like provide excellent chemical inertness, high service temperature, high strength and durability. A coating of a fluorocarbon material that is adapted with good adhesion to the underlying substrate material protects the substrate material from aforementioned weaknesses, thereby significantly increasing the service life of the substrate material. Likewise, an elastic sleeve member coated with a fluorocarbon material will benefit from the chemical inertness, high service temperature, high strength and durability of the fluorocarbon, resulting in a longer service life for the sleeve member.
Polytetrafluoroethylene is commercially sold by E.I. DuPont Nemuors and Company under its registered trademark “Teflon” and by Polymer Corporation under the registered trade name of “PolyPenco.” Polyvinylidene fluoride is commercially sold by Elf Atochem North America, Inc. under its registered trademark of “Kynar.” Polytrifluorochloroethylene is commercially sold by M.W. Kellogg under its registered trademark “Kel-F.”